:root {
    /* Microsoft Fluent Design System Colors */
    --primary-color: #0078d4;
    --primary-light: #106ebe;
    --primary-dark: #005a9e;
    --secondary-color: #605e5c;
    --accent-color: #ff6b35;
    --success-color: #107c10;
    --danger-color: #d13438;
    --warning-color: #ff8c00;
    
    /* Neutral Colors */
    --surface-color: #ffffff;
    --surface-secondary: #f3f2f1;
    --surface-tertiary: #edebe9;
    --text-primary: #323130;
    --text-secondary: #605e5c;
    --text-disabled: #a19f9d;
    
    /* Dark Theme Colors */
    --dark-surface: #1b1a19;
    --dark-surface-secondary: #2d2c2c;
    --dark-surface-tertiary: #3b3a39;
    --dark-text-primary: #ffffff;
    --dark-text-secondary: #c8c6c4;
    
    /* Shadows */
    --shadow-1: 0 1px 3px rgba(0, 0, 0, 0.12), 0 1px 2px rgba(0, 0, 0, 0.24);
    --shadow-2: 0 3px 6px rgba(0, 0, 0, 0.16), 0 3px 6px rgba(0, 0, 0, 0.23);
    --shadow-3: 0 10px 20px rgba(0, 0, 0, 0.19), 0 6px 6px rgba(0, 0, 0, 0.23);
    --shadow-4: 0 14px 28px rgba(0, 0, 0, 0.25), 0 10px 10px rgba(0, 0, 0, 0.22);
    
    /* Spacing */
    --spacing-xs: 4px;
    --spacing-sm: 8px;
    --spacing-md: 16px;
    --spacing-lg: 24px;
    --spacing-xl: 32px;
    --spacing-xxl: 48px;
    
    /* Border Radius */
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    color: var(--text-primary);
    line-height: 1.6;
}

/* App Container */
.app-container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* Header */
.app-header {
    background: var(--surface-color);
    box-shadow: var(--shadow-2);
    padding: var(--spacing-sm) 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-lg);
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: var(--spacing-md);
}

.app-title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--primary-color);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.app-title i {
    font-size: 1.25rem;
}

.game-stats {
    display: flex;
    gap: var(--spacing-lg);
    flex-wrap: wrap;
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.stat-label {
    font-size: 0.875rem;
    color: var(--text-secondary);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.stat-value {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
}

/* Main Game Area */
.game-main {
    flex: 1;
    padding: var(--spacing-xl) var(--spacing-lg);
    max-width: 1200px;
    margin: 0 auto;
    width: 100%;
}

.game-container {
    display: grid;
    grid-template-columns: 1fr 350px;
    gap: var(--spacing-xl);
    align-items: start;
    max-width: 1000px;
    margin: 0 auto;
}

/* Game Board */
.game-board-container {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-3);
    overflow: hidden;
    transition: all 0.3s ease;
}

.game-board-container:hover {
    box-shadow: var(--shadow-4);
    transform: translateY(-2px);
}

.board-header {
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-md) var(--spacing-lg);
}

.board-header h2 {
    font-size: 1.25rem;
    font-weight: 600;
    margin: 0;
}

.canvas-wrapper {
    padding: var(--spacing-lg);
    display: flex;
    justify-content: center;
    background: var(--surface-secondary);
}

#game-board {
    border: 3px solid var(--primary-color);
    border-radius: var(--radius-md);
    background: #000;
    box-shadow: inset 0 0 20px rgba(0, 120, 212, 0.1);
}

/* Sidebar */
.game-sidebar {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.sidebar-section {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-2);
    overflow: hidden;
    transition: all 0.3s ease;
}

.sidebar-section:hover {
    box-shadow: var(--shadow-3);
    transform: translateY(-1px);
}

.section-title {
    background: var(--surface-secondary);
    color: var(--text-primary);
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: 1rem;
    font-weight: 600;
    margin: 0;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
}

.section-title i {
    color: var(--primary-color);
}

/* Next Piece */
.next-piece-container {
    padding: var(--spacing-lg);
}

.next-piece-container h4 {
    margin-bottom: var(--spacing-md);
    color: var(--text-secondary);
    font-size: 0.875rem;
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

#next-piece {
    border: 2px solid var(--surface-tertiary);
    border-radius: var(--radius-sm);
    background: #000;
    display: block;
    margin: 0 auto;
}

/* Controls */
.controls-grid {
    padding: var(--spacing-lg);
    display: grid;
    gap: var(--spacing-md);
}

.control-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: var(--spacing-sm) 0;
    border-bottom: 1px solid var(--surface-tertiary);
}

.control-item:last-child {
    border-bottom: none;
}

.control-key {
    background: var(--primary-color);
    color: white;
    padding: var(--spacing-xs) var(--spacing-sm);
    border-radius: var(--radius-sm);
    font-size: 0.75rem;
    font-weight: 600;
    min-width: 60px;
    text-align: center;
    box-shadow: var(--shadow-1);
}

.control-desc {
    color: var(--text-secondary);
    font-size: 0.875rem;
}

/* Action Buttons */
.action-buttons {
    padding: var(--spacing-lg);
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.btn {
    padding: var(--spacing-md) var(--spacing-lg);
    border: none;
    border-radius: var(--radius-md);
    font-family: inherit;
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    box-shadow: var(--shadow-1);
}

.btn:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-2);
}

.btn:active {
    transform: translateY(0);
    box-shadow: var(--shadow-1);
}

.btn-primary {
    background: var(--primary-color);
    color: white;
}

.btn-primary:hover {
    background: var(--primary-light);
}

.btn-secondary {
    background: var(--secondary-color);
    color: white;
}

.btn-secondary:hover {
    background: #4c4a48;
}

.btn-danger {
    background: var(--danger-color);
    color: white;
}

.btn-danger:hover {
    background: #b02a2e;
}

/* Responsive Design */
@media (max-width: 1024px) {
    .game-container {
        grid-template-columns: 1fr 300px;
        gap: var(--spacing-lg);
    }
    
    .header-content {
        flex-direction: column;
        align-items: flex-start;
        gap: var(--spacing-md);
    }
    
    .game-stats {
        width: 100%;
        justify-content: space-between;
    }
}

@media (max-width: 768px) {
    .game-container {
        grid-template-columns: 1fr;
        gap: var(--spacing-lg);
    }
    
    .game-sidebar {
        order: -1;
    }
    
    .game-stats {
        flex-direction: column;
        gap: var(--spacing-sm);
    }
    
    .stat-item {
        flex-direction: row;
        justify-content: space-between;
        width: 100%;
    }
    
    .app-title {
        font-size: 1.5rem;
    }
    
    .stat-value {
        font-size: 1.25rem;
    }
    
    #game-board {
        width: 100%;
        max-width: 300px;
        height: auto;
    }
    
    .canvas-wrapper {
        padding: var(--spacing-md);
    }
}

@media (max-width: 480px) {
    .game-main {
        padding: var(--spacing-md);
    }
    
    .header-content {
        padding: 0 var(--spacing-md);
    }
    
    .action-buttons {
        flex-direction: row;
        flex-wrap: wrap;
    }
    
    .btn {
        flex: 1;
        min-width: 120px;
    }
}

/* Dark Theme Support */
@media (prefers-color-scheme: dark) {
    :root {
        --surface-color: var(--dark-surface);
        --surface-secondary: var(--dark-surface-secondary);
        --surface-tertiary: var(--dark-surface-tertiary);
        --text-primary: var(--dark-text-primary);
        --text-secondary: var(--dark-text-secondary);
    }
    
    body {
        background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
    }
}

/* Animation for game elements */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.sidebar-section {
    animation: fadeIn 0.5s ease-out;
}

.sidebar-section:nth-child(2) {
    animation-delay: 0.1s;
}

.sidebar-section:nth-child(3) {
    animation-delay: 0.2s;
}

/* Focus states for accessibility */
.btn:focus,
.control-key:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* Loading state */
.loading {
    opacity: 0.7;
    pointer-events: none;
}

/* Game over overlay */
.game-over {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.8);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
}

.game-over-content {
    background: var(--surface-color);
    padding: var(--spacing-xl);
    border-radius: var(--radius-lg);
    text-align: center;
    box-shadow: var(--shadow-4);
    max-width: 400px;
    width: 90%;
}

.game-over-content h2 {
    margin-bottom: var(--spacing-md);
    color: var(--danger-color);
    font-size: 1.5rem;
    font-weight: 600;
}

.game-over-content p {
    margin-bottom: var(--spacing-sm);
    color: var(--text-secondary);
    font-size: 0.875rem;
}

.game-over-content .btn {
    margin-top: var(--spacing-lg);
    width: 100%;
    max-width: 200px;
}